Composite piston and method for making same



July 9, 1935. Q. TEETOR 2,007,839

COMPOSITE PISTON AND METHOD FOR MAKING SAME Filed Aug. 24, 1932 2 Sheets-Sheet 1 July 9, 1935. M. o. TEETOR 2,007,839

COMPOSITE PISTON AND METHOD FOR MAKING SAME Filed Aug. 24. 1932 2 Sheets-Sheet 2 Patented July 9, 1935 v r 1,007,839 PA ENT OFFICE I COMPOSITE PISTON AND METHODFOR r l MAKING' SAME- Macy-0. Teetor, Newcastle, 1nd,; assignorito ilhe Perfect Circle Company, Hagerstown, Indiana, a corporation of Indiana Application August 24, 1932, Serial No. 630,180

Claims. 29-45 65) This invention relates to pistons and the like and more particularly to composite pistons for internal combustion engines and the like. The principal object of my invention is to provide a piston having a headand a skirt in constant axial alignment with the connecting means so arranged that the head expands freely without distorting the skirt which is fitted in the cylinder with minimum clearance. I

i More specifically, I provide a piston having aheadformed of light material, such as aluminum alloyyand a closely fitting skirtofhardermaterial andhaving a lesser coeificient oi expansion,

such as cast i'rcnand provide struts for connect 1 ing the head and skirt together so that the head may expand 1 fre'ely independently of the skirt while at thesame timethe head is maintained proper axial alignment with respect to the skirt iifurther object of my invention is to provide a novel method of casting such a piston. According to 'my method the aluminum head is flrst cast on to suitable struts having the'clesired coefficient of :expansion and then the iron-skirt iscast on to the struts. Further theskirt is cast out of round to provide for shrinkage in the iron, the skirt.

when finished, being perfectly circular with the walls/Lot properl'thickness. r i r i The above {and other objects or my invention will become apparent from. the" following de scription takenin conjunction with theaccompanying drawings-fin which:

:H'Eigure 1 is a longitudinal vertical section through apiston embodying one'torm or my invention; Fig.. 2'-is' a vertical section taken on the line Fig. 3risn ahorizontal section'. taken on the line 7 3-43 or Fig. 1;;

L Fig.-:4. is avertical secti on taken through the; casting. forming the 0 head .before it is machined g. Fig; 5 is a, horizontal section corresponding: to

that of Fig. 3exce'pt that-the str utsare broken away and the section illustrates-the skirt at the time it is cast and before theiron cools, and W Fig. 6 is a iragmentaryview showing a portion oftthe skirt in top plan.

The head 6 when finished, as shown in Figs. 1

and 2., is-provi'ded with the usuaL-piston ring groove! and has two dependingarms or hangers pansioh,l.such.as cast-iron, and is connected to the hangers 8 of the head by two lower supporting struts l2 and two bracing struts 13.

metal carrying two tubular anchoring pieces l5; The struts I2 are preferably formed of a wide strip of metal having a low coeflicient of expansion which maybe the same as, or slightly lower than, that of the skirt. Openings, surrounded by flanges l6, are formed in the central portion of eachstrut l2 and the tubes l5 are driven into these openings in which they have a tight press fi-t. Each of the'bracing struts I3 is in the form of anarrow strip of metal having the same coefiicientot expansion as the struts l2. In fact, the struts i2 and I3, associated with each hanger 8, are preferably formed of one piece of metal and are connected together by the vertical connectinghar lll, the metal at'the point of'union of the bar and strut heing bent at right angles so that the strut l3 lies in a horizontal plane.

In making the piston, the supporting struts l2 and the bracing struts l3 are suitably supported in a sand orpermanent'mould and the aluminum is then poured intothe mould to form the un--] finished casting as illustrated in Fig. 4. Theinner en-chef ,theistruts [3 are imbedded in the hangers-i 8- above the bosses and these ends are bentdownwafdly and provided with holes [8 to better anchorthem in the hangers; The lower ends of thehangers are cast around the centers of the struts l2 and the tubes l5 which firmly anchor. the struts l2 in the hangers and prevent anyrelative movement between them. After the aluminum coolasthe skirt is then cast onto the struts in a suitable mould, the skirt havingthe interior." projections which are'cast around the outer ends of the struts l3 (Figs. 1 and 6) and theprcjectionszl (Figs. 1 and 3) which are cast around the ends of the struts l2. The outer ends oftthe struts l3 and the ends of struts l2 like wise have holes which serve to better anchor them to the skirt. A washer 23* (Fig. 4) of asbestosor other suitable material is placed on the end of the flange of the head casting so that when the skirt is cast the cast iron does not come into contact with the head. After the pistonis com-V pletely'cast 'it i's machined and finished.

i Inoperation of the piston an engine, the head, due-to its greater coefiici'ent of expansion and thehhigher temperature to which it is subjected; expands to agreat'er degree than the skirt." During this expanding action, the hangers 8 move apart, and during this movement the hangers, as well the supporting struts; Il and the bracing struts l3 so that this srpsnsion is riot trans mitted to the skirt roper and the latter is not distorted. 'I'he struts l3 maintain the head in axial alignment with the skirt which is desirable .tor'eificierit' operation ortne engine. Further,

the head. rocked-relative to the shirt the lower ends of the hangers and the ends of the struts I2 would'be subjected to shearing strains result Each supporting strut l2 comp-rises a flat bar of ing in loose points of connection or breakage.

I find that it is advantageous to connect the struts !3 to the struts 12, as" by the bars l9, so

that the vertical flexing of the struts 13 does not" Without such connections when aiTect the skirt. the hangers are elongated the upper movement of the struts l3 would tend to distort the skirt slightly adjacent the projections 20, thus causing high spots. With the bars I9 thisobjection is elimi nated.

I have found that with the above described structure, the skirt may have a constantly close fit in the cylinder without undue distortion and that the head is maintained in proper axial alignment on the skirt, thus eliminating objections to which other pistons are subject.

I have found that, when a cast iron skirt is cast directly on an aluminum head or the hangers thereof, the aluminum will either melt or form an oxide at the points of union with the result that the piston is defective; I have also found that it is necessary to anchor the hangers of an aluminum head at more than one point to the skirt but that when the aluminum hangers of the head are cast on to struts which are already anchored at their ends in the skirt, the subsequent shrinkage of the aluminum is likely to cause excessive distortion and loose joints at the anchorage points as the metal cools.

In my method, I first connect the hangers of the aluminum head to each strut at one point only so that the aluminum has every opportunity to shrink around the struts without cracking or without imposing strains on any other parts of the casting. I then cast the iron skirt on to the ends of the struts and during the shrinkage of the cast iron, the flexibility of the struts prevents undue strains-from being placed on the hangers or head. a

I have found by actual experience that when the skirt shrinks after casting it would become slightly oval if cast circular and with the wall of uniform thickness. Obviously the skirt, when finished, must be round to fit the cylinder. In order to accomplish this circularity, which is shown in Fig. 3, I cast the skirt slightly-oval and with tapering wall thicknesses as illustrated in Fig. 5 and then, upon cooling, the interior of the cylinder becomes circular and machining of the exterior brings this exterior into circularity and into concentricity with the interior. This will be clearer from the following explanation, with particular reference to Fig. 5 which shows a cross section through the skirt as it is in the mould cavity and before cooling of the casting. The inside diameter A, which is at right angles to the struts i2 is slightly larger than the uniform inside diameter of the skirt after it shrinks and the diameter B is slightly smaller. The wall of the skirt casting, as shown in Fig. 5, is thickest at bb and tapers both ways, being thinnest at aa. When the'casting cools, each strut l2 tends to fixedly hold the projections 2|, in which its ends are imbedded, from moving toward each other, or, as it might be expressed, the struts tend to prevent the skirt from shrinking in the direction of the struts. The arcs cc of the wall, being longer than the arcs dd tend to straighten out and the inside diameter on the line A is reduced to the final inside dimension. At the same time the points bb move slightly further apart which increases thediameter on which these points lie so that the inside of the piston becomes circular instead of remaining oval. Of course, as the wall thickness varies the exterior of the skirt is oval after the casting cools, but it is made circular in the machining operation as the most metal is removedwhere the walls are the thickest and when the skirt is finished it is circular and the inside and outside walls are concentric.

It is understood that the structure and method may be modified without departing from the scope of the invention.

I claim:

1. In a piston, a head having depending hangers, a separate skirt, cross struts flexible only horizontally of the piston and having their central portions connected to the lower ends of said hangers and their opposite ends to the skirt, bracing struts flexible vertically and connected at their inner ends to the upper portions of the hangers and at their outer ends to the skirt and means connecting the bracing and cross struts.

2. In a piston, a head having depending hangers, a separate skirt, cross struts formed of flat metal flexible only horizontally of the piston and having their central portions connected to the lower ends of said hangers and their opposite ends to the skirt, and bracing struts formed of flat metal'lying in a horizontal plane flexible vertically and connected at their inner ends to the upper portions of the hangers and at their outer ends to the skirt, and bars connecting the cross and bracing struts, each bar and the connected cross strut and bracing strut being formed of one piece of metal.

3. In a piston, a head having depending hangers, a separate skirt, cross struts formed of flat metal flexible only horizontally of the piston and having their central portions connected to the lower ends of said hangers and their opposite ends to the skirt, bracing struts flexible vertically and connected at theirinner ends to the upper portions of the hangers and at their outer ends tothe skirt, and bars connected at their lower ends to the cross struts and their upper ends to the bracing struts intermediate the ends of the latter.

4. The methodof making a piston Which con sists in placing struts in a mold, casting the head and its hangers so that the hangers are cast around portions of the struts, next casting the skirt out of round on to ends of the struts, then permitting the skirt to shrink, the skirt interior being thereby brought into circularity, and finally finishing the exterior of the piston. I

5. The method of making a piston'which consists in placing struts having a'low coeflicient of expansion in a mold, casting the head and its hangers having a high coefficient of expansion so that the hangers are cast around portions of the struts, next casting the skirt out of round and with walls of varying thickness on to ends of the struts, then permitting the skirt to shrink the interior being thereby brought into circularity, and finally finishing the exterior of the skirt to bring the exterior of the skirt into circularity and concentricity with the interior of the skirt.

MACY o. 'I'EETOR. 

